Effects Of Welding Process On Hydrogen Induced Failure Behavior Of 304 Stainless Steel Weld Seam

Austenitic stainless steel weld seam is an important connection structure in hydrogen energy storage and transmission system.Its long-term service in the hydrogen environment will cause hydrogen embrittlement such as plasticity loss and accelerated fatigue crack growth rate,which seriously endangers the safety of the high-pressure hydrogen system.Therefore,in order to ensure the safe operation of the high-pressure hydrogen system,it is necessary to study the hydrogen embrittlement of austenitic stainless steel weld seams.This paper takes 304 austenitic stainless steel MIG weld seams and TIG weld seams as the research object,uses mechanical performance evaluation methods,electrochemical hydrogen charging technology,microcharacterization and other methods to study the influence of welding processes on the microstructure of 304 stainless steel weld seams,and explores the influence of microstructure evolution on hydrogen embrittlement susceptibility of 304 stainless steel weld seams.The main research work is as follows:(1)The influence of welding heat input on the microstructure and properties of the weld is studied.The results show that the ferrite structure of MIG welds is mainly lath and dendritic,while ferrite in TIG welds mainly presents dendritic,strip and network structures;the strength and plasticity of MIG and TIG welds both increase first and then decrease with the increase of welding heat input.The mechanical properties of MIG welds are better when the heat input is8.6k J/cm,and the mechanical properties of TIG welds are better when the heat input is14.966 k J/cm.MIG welds fracture mainly by tearing and micro voids coalescence in air environment.In addition to tearing and micro voids coalescence,TIG welds also have a small amount of trans-granular fracture.(2)The hydrogen distribution characteristics of MIG welds and TIG welds and the hydrogen-induced microstructure evolution mechanism are discussed.The results show that the ferrite in the MIG weld and TIG weld first reaches saturation during the hydrogen charging process,and then hydrogen atoms diffuse into the austenite.However,due to the low diffusion coefficient of austenite,hydrogen atoms tend to be enrichment at the ferrite-austenite interface;after 304 stainless steel is welded,the grains of the MIG weld are obviously coarsened,and the columnar crystals of the TIG weld are more oriented and the degree of grain coarsening is lower;after hydrogen charging,the grain size of the MIG weld seam and the TIG weld seam are slightly increased.(3)The hydrogen embrittlement susceptibility of MIG weld seams and TIG weld seams under different welding processes is explored.The results show that the 304 stainless steel MIG weld seams and TIG weld seams under the action of hydrogen have obvious plastic loss,and the hydrogen embrittlement resistance of the welds first increases and then decreases with the increase of welding heat input;The resistance to hydrogen embrittlement of TIG weld seams is better than that of MIG weld seams,and the weld seams with dendritic ferrite structure are more resistant to hydrogen embrittlement,while the welds mainly made of lath ferrite have weaker hydrogen embrittlement resistance;after hydrogen charged,the fracture modes of MIG weld seams are a small amount of intergranular fracture,cleavage/quasi-cleavage and micro voids coalescence,and the fracture modes of TIG weld seams are intergranular fracture,cleavage/quasi-cleavage and micro voids coalescence.